1. Field of the Invention
This invention relates to a system for measuring and displaying unbalance in a rotating body and more particularly to such a system which has the capability of measuring and compensating for system imposed unbalance measurement errors.
2. Description of the Prior Art
Vibration vector measurement for determining unbalance in a rotating body is well known. For example, U.S. Pat. No. 3,220,247, issued to Goodman, discloses apparatus for obtaining such measurements which includes an unbalance pickup device which provides signals indicative of the unbalance or vibration vector in the rotating body. Sine and cosine generators are also provided which generate reference signals with reference periods which are the same as the periods of the unbalance signals. The unbalance signals and the reference signals are coupled to multipliers and the resulting products are passed through filtering circuits to obtain average or mean values. An analog circuit implementing Fourier analysis to process the unbalance signals in analog form and to thereby obtain the unbalance vector magnitude and direction is also disclosed in the Goodman patent.
In U.S. Pat. No. 3,751,987, issued to Whitmore, a dynamic balancing machine is disclosed which includes an electronic circuit coupled to transducers which sense the unbalance and provide unbalance signals. A reference detector is also provided to indicate a zero angle reference for the rotating portion of the balancing machine. Sine and cosine signals are produced relative to the reference signal, and an analog multipler circuit multiples the unbalance signal with the sine and cosine reference signals thereby providing product outputs which are subsequently filtered. The filtered product outputs represent means values which are displayed as indicators of the magnitude and angular location of the unbalance force. This method of extracting the sine and cosine coefficients from an unknown periodic unbalance force to obtain the magnitude and direction of the unbalance force has long been in use. U.S. Pat. No. 4,015,480, issued to Giers, discloses such a system wherein a portion of the signal processing is done in digital fashion. Reference sine and cosine values having an oscillation frequency which is the same as that of the unbalance vibration are digitized together with the unbalance signals and are thereafter multiplied to provide sine products and cosine products. The sine and cosine products are summed, means values are extracted from the two sums, and the mean values are utilized to identify the magnitude and phase of the unbalance.
U.S. Pat. No. 4,046,017, issued to Hill, discloses a dynamic wheel balancing apparatus having a rotating shaft on which the body to be balanced is mounted together with a pair of force transducers adjacent to the shaft which provide signals representative of the unbalance in the body. The apparatus further includes circuitry which provides pulses corresponding to rotational increments of the shaft. A counter is provided which counts the pulses starting from the time when the unbalance force produced by the rotating body passes through a particular angular position such as the vertically upward position. The shaft is spun, the counter is actuated to count pulses, the counter output is converted to an analog signal, the analog signal is stored, and the shaft is stopped. The wheel is thereafter rotated by hand until an angular position meter indicates the shaft is in the angular position at which the unbalance in the body was measured. At initial installation the rotating shaft on which the unbalanced wheel is to be mounted is mechanically balanced to eliminate error insertion. A subsequent replacement of the spin shaft requires mechanical rebalancing of the machine. Mechanical and electrical adjustments sometimes being interactive, a trained person is usually required to set them in the machine.
It is desirable to provide an unbalance force measuring machine and method which may be calibrated by the machine operator and which provides highly accurate unbalance vector readings which are substantially unaffected by mechanical and electrical component drift.